Cabs of heavy motor vehicles are known to comprise substantially a a pair of side panels each housing a door, a front panel, a rear panel and a roof panel. These panels, normally of sheet metal, are joined rigidly together by welding to define a rigid structure of high mechanical strength, to form the compartment for the vehicle driver. A floor panel also forms part of the cab and is shaped in such a manner as to form below it a housing for the upper part of the vehicle power unit. Said cab can be tilted relative to the vehicle frame about a transverse shaft positioned at the front of the frame, to give easy access to the power unit and to the main mechanical members of the vehicle.
Normally the lower parts of the cab front and side panels are shaped to shield the front and sides of the vehicle frame and some of the mechanical members connected to it. This shielding action is also partly provided by the bumper and side cab access footboards normally fixed to the vehicle frame.
The dimensions of cabs for heavy motor vehicles belonging to one and the same series but designed for the transportation of different loads vary according to the height of the vehicle axles from the ground and the dimensions of the power unit and other main mechanical members. Consequently the cabs of vehicles designed for transporting the larger loads are of larger size, and in particular have a larger overall height. This is a consequence mainly of the fact that in addition to forming a compartment for the driver, the cab must also shield the front and sides of the vehicle frame and main mechanical members, the vertical dimensions of which are greater than in the case of vehicles designed for transporting small loads. The result is that the height of the front, side and rear panels of a cab is greater in those vehicles designed for transporting the greater loads. Consequently the equipment necessary for constructing all the cabs required for use on a given series of heavy vehicles with capacities varying within a fairly wide range is considerable, complicated and very costly. In addition, the number of mechanical parts which have to be held in store to satisfy cab production and subsequent spares requirements is very large.